Please consider donating to help us continue to serve you.
Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
||Thread Tools||Search this Thread|
|22nd April 2018, 01:19 AM||#1|
Join Date: Nov 2016
Two mid-sized TH, vs four smallish BR?
I need to discuss this rather badly. The same dilemma tons of bands & "event" DJ's face. Some folks say horns are the obvious choice, and maybe so, but I'm not so sure.
I'm going to lay out the pros & cons as I currently see them, and hopefully you guys can correct any mistakes, and / or add any opinions.
The main thrust of this is the fact that small horns, even TH, are always a bit of a trade-off on LF extension. Granted, for this type of sound reinforcement, it may or may not be needed to go very low. Heck, it may not be necessary to have much below 50 Hz, I don't know, BUT IT CERTAINLY DOESN'T HURT.
So here's how I see it, right now:
Folded horns: Forget it, too big, and if smallish, WAY too much LF loss unless you use a lot of them. Just no.
Tapped Horn: Obviously better LF extension than a folded, but still marginal.
Danley's THMini (his smallest single 12") is -3dB at 48Hz. Not horrible, but forget that Ragga party you had planned.
Grouping TH horns gives more output, but not much extra LF extension. So, the best one can do is electronic (EQ) compensation, and then lower the output.
This could work, but then you need more physical subs, so you're losing a main advantage of horns which is efficiency. Also, small TH tends to drop off a cliff on the bottom, so you have to be very careful with your HPF and excursion control, plus maybe that doesn't sound so good?
Efficiency: The horns main ace in the hole, no doubt, even with heavy EQ. IMO, this is more important for saving amps needed, for a given output, than for saving space.
Sound Quality: Hmmm. Everybody like the speed and tightness of a good horn. No argument form me. However: (& PLEASE CORRECT ME IF I'M WRONG)
It seems to me that the main reason for this is that, because the horn is so efficient, you have much less cone movement for a given dB. thus, all sorts of distortion are minimized, and apparent "speed" is increased as well.
But this brings me to BR, and why they might not be so much worse:
The lowly Bass reflex:
I will only talk about P-P and PPSL, since any other BR is going to be too muddy. Let's also assume that we have a proper slot port, so no chuffing or other artifacts.
This type sub has two advantages over a TH: LF extension in a smallish package, and (probably) lower even order harmonic distortion. (Mind you, I'm not super-clear on the physics behind horns, so again, correct me if I'm wrong.)
The "obvious" downside of a PPSL BR are efficiency, and possibly a "slower, less tight" sound.
BUT IS THAT REALLY SO? ## THIS IS THE MAIN REASON FOR THS THREAD:
Forget the power requirements advantage of horns. There's no getting past that. But let's say you have enough power for either system. You got the amplifiers at the gig, and you've got the amps in the wall outlet. Now you have to decide on a design, based on packing room in your truck, and desired sound quality.
What I'm thinking is this:
If you build a TH (even a Keystone) large enough to have really solid LF extension, the thing is going to be nearly twice the size of a BR enclosure using the same drivers, with the same LF extension. (and the BR could go even lower if built a little bit larger.) So lets just say for arguments sake that you can load four dual 15" PPSL BR's, or two smallish 15" TH's:
It's said that a horn design is typically 6dB more efficient than a BR. OK, that's the equivalent of twice as many drivers in a BR setup. WHICH IS EXACTLY WHAT WE'RE COMPARING. Again, forget the power requirements.
For a given output level at, say 50 Hz, would not the two drivers in the BR design be moving about the same exact amount of excursion as the single driver in the horn?
You see where I'm going with this. If that's true, then:
### FOR A GIVEN VOLUME, shouldn't the dual-driver PPSL BR sound very similar to the single-driver horn, in terms of tightness and lack of modular distortion?
- And the PPSL BR design has the added advantage of extreme reduction in even order distortion, whereas PPSL would be VERY hard to do with a smallish TH horn. (Though I'd love to see a smallish PPSL TH design. )
- AND you'd still probably have better LF extension than with the smallish TH, and certainly a smoother LF roll off.
It seems to me that the trick with designing the "ultimate" BR PPSL enclosures for your personal needs is to find the perfect trade-off between enclosure size, (determining the LF extension you want) and getting as much total cone area as possible, so as to minimize excursion. (You'd also have significant built-in headroom, should you ever need it.
The only significant downside is the need for more amplifier power.
And a final thought: I was speaking to Jeff at JTR a few weeks ago, as I was surprised he'd retired his well-respected "Growler" horn and basically replaced it with a 2X12" BR design. (not even push-pull.) He told me that his reason was the 2X12 was more efficient (101 dB) smaller & lighter, and everyone (typically using 2 or more of them) thinks it sounds just as good, if not better. OK, his words, not mine, but there you go.
But again, this is all 100% theoretical. I could be pretty far off, but I know that all of the above is at least PARTIALLY correct.
So please, have at it. Rip my thoughts to shreds if I'm totally wrong, but I need to get a better understanding of all this, without actually building a bunch of subs first.
Last edited by Cableaddict; 22nd April 2018 at 01:22 AM.
|22nd April 2018, 04:06 AM||#2|
Join Date: Jan 2008
2) TH and BR both typically drop at 24 dB per octave below Fb, as do most "undersized" FLH. One can design any of these three types for less drop off below Fb/Fc, with a resultant penalty in output at the low corner.
3)Given double the amps and drivers, a slight space savings can be had using BR compared to TH.
4) OK- I'll correct you.
Given a horn and a BR with the same frequency response, they will sound quite similar regarding "speed and tightness", distortion has little (like effing nothing) to do with "speed and tightness".
5)"Muddy" BR generally have weak magnets, little Xmax and a narrow peak around Fb.
"Proper" ports can be slot shaped, round, triangular, square, trapezoidal, or any shape with enough enclosed volume to keep the slug of air from spilling out "at speed".
6)BR and TH LF extension vs. size is quite driver dependent, but generally speaking, for small enclosures go for BR if LF around FB is most important, TH if upper bass output more important.
7) See response #4.
8) Assuming both had the same FR, the excursion of the 2 drivers in the BR would be similar at 50 Hz to the single driver in a TH at 50 Hz.
9) There is no such thing as "modular distortion", unless you squash an IKEA ;^).
In terms of AM (amplitude modulation) distortion, at a given excursion, it would be equal in both designs.
10) The reduction would be dependent on the driver, one can't measure "extreme reduction" if the driver is clean to start with.
11) I designed the Keystone Sub to have the same LF extension as the BR cabinets it replaced, the LF roll-off was nearly identical.
Bottom line- the pair of Keystone subs weighed less, had the same LF output of four dual LAB12 subs of exactly the same exterior dimensions, and far more upper response using the same amplification.
When I crammed a pair of Dayton 15" into a PPSL version of the same BR cabinet (1/2 the size of the Keystone)
Compact 2x15" PPSL Using Dayton PA385-8 Drivers
compared to the Keystone LF output at 40Hz was -3dB for a pair of the 2x15" PPSL, 60 Hz range increased by 5 dB, response around 100Hz near equal, using double the power.
Distortion (both even and odd) with the Dayton PA385 was far higher in the PPSL than the LAB 12s in standard BR or in the Keystone, and the B&C18SW115-4 less then the LAB 12s.
|22nd April 2018, 10:02 AM||#4|
Join Date: Feb 2008
Have you HEARD a good bass reflex subwoofer, or are you basing all this on your experience with sub-par equipment?
Well-designed BR cabs with good drivers sound good.
Poorly designed BR cabs with cheap drivers sound bad.
Any speaker driven to its limits sounds bad.
Same goes for TH, PPSL, FLH, BLH, sealed boxes, IB, OB, all variations on the QWT, those weird BR/horn hybrids... Any cabinet you can think of. Get some good drivers in some cabinets that are designed and built well, and your sound will be many miles ahead of where you are now.
To my recollection, you still haven't actually said where you are in the world. Chances are there's a good bass reflex cabinet near you, that you can go and audition if you ask nicely.
So far you've tried:
- A bunch of 18"s in sealed boxes, and wondered why they're so power hungry
- Some cheap over-driven 12"s, and wondered if PP mounting will save them.
I'll say this one last time: start with your design goals and work from there. All cabinets are compromises, and you need to decide which compromises will suit you best. In order to do that, you need a clear list of what you want to achieve with your new subwoofers.
I'd suggest that what you're looking for is similar to what I was looking for around a year ago:
- 40Hz extension
- Compact, for a PA subwoofer
- As loud as possible while keeping the above.
What you do not need is yet another long post where you go around in circles.
Start a new thread, and state exactly what you'll be using the new subs for, and include any other relevant information (like power available, budget, etc).
Until you start that thread, I won't be replying to your threads any more. Life's too short.
|22nd April 2018, 12:04 PM||#5|
Join Date: Sep 2016
TH is DSP dependent, while BR is easy to integrate with tops, you can implement it with single passive or active crossover, so for DJ use and considering back up, TH is little more expensive.
To buld TH are much more complex and requires more woods, glue, etc resulting it little more expensive too.
But at the end TH is more efficient and give more SPL from the save amp voltage.
Remember to think about how many cab you can connect to you amp or you and up needing more amp to supply more cabs.
This additional comments added to what art and chiss said will be target dependent, so think about it
|22nd April 2018, 04:47 PM||#6|
Join Date: Dec 2010
but i have to say the simple BR's that I built sound every bit as good,
as the PPSL and push-push SL I've been posting about.
|22nd April 2018, 11:43 PM||#7|
Join Date: Nov 2007
BR suffer from two issues that you won't typically see in a software generated response curve.
1. Power compression (vent)
around the resonance frequency. The vent is producing the majority of the speaker's output at and around Fb, and the smaller the cross-section of the vent, the more this compression will be. My POC6 MLTL, which is basically a vented box with an extra internal panel, displays up to 2dB of compression at Fb, and the "vent" in this case is two-thirds of the driver's Sd, and the driver only has 5mm Xmax. I suspect that power compression will be higher than that at peak levels for BR boxes with smaller vents and where drivers with higher Xmax are used.
For comparison purposes, a subwoofer using the same driver in a TH alignment experienced only 0.3dB of compression at Fb when run at peak levels (distortion reaching 10% in the passband).
I think the lower power compression of the TH compared to the BR design contributes a lot towards what I perceive to be the "effortless sound" of a TH. The MLTL I built also sounds pretty decent, but bear in mind the huge vent size - 350cm^2 for a 12" driver.
There are of course BR designs that use large vents, but the larger the vent, the more the impact it will have on the midbass response of the speaker due to the vent resonance modes, unless perhaps you design it like an MLTL like I did, and use the physical layout of the box to move the impact of the vent resonances out of the subwoofer's passband. And of course a larger vent does mean a larger box.
2. Power compression (thermal).
Typical BR designs have the driver mounted with the motor inside of the box, as opposed to THs, where the driver is facing into the path and the motor is located in the mouth. Theoretically this should result in better cooling for the motor, and the cooler the motor, the less the impedance of the voice coil will rise at high power levels, which should result in less power compression.
|23rd April 2018, 07:35 AM||#8|
I do not understand the size vs low frequency efficiency argument. A same size TH/BR comparison will often give near equal low frequency extension. The BR will have some other benefits though (at least if it's done right).
Air speed/particle velocity in relation to power applied should always be a consideration when calculating the design, you can see this in hornresp easily.
Brian: Good point about reverse-mounting the drivers for high power applications!
|Thread Tools||Search this Thread|
|Thread||Thread Starter||Forum||Replies||Last Post|
|Smallish 30Hz PA||Zwiller||PA Systems||20||19th July 2017 03:23 PM|
|JBL smallish PA-sub with a car-woofer||TroelsM||Subwoofers||13||13th June 2016 12:35 PM|
|2-way + sub or 3-way + sub in a smallish room||VEC7OR||Multi-Way||23||1st March 2011 04:28 PM|
|need a smallish 24v 5A power supply ..||onis_uk||Power Supplies||3||29th August 2010 03:12 PM|
|Smallish IB setup||Timn8ter||Multi-Way||5||27th September 2003 02:11 PM|
|New To Site?||Need Help?|